Optical pickup

ABSTRACT

An optical pickup is provided for driving objective lenses in focusing and radial directions. The pickup includes a movable member, and objective lenses at the center portion of the movable member. The pickup also includes coil blocks provided at two side portions of the movable member, and pairs of magnets flanking the coil blocks in a tangential direction perpendicular to the focusing and radial directions. Support members are attached to the side portions of the movable member, permitting the movable member to move in the focusing direction and the radial direction. Each coil block includes focusing and tracking coils for driving the movable member in the focusing direction and the radial direction. The center portion of the movable member, below which a reflector is arranged, is thinner than the side portions of the movable member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an optical disc device to perform recordingonto and reproduction from an optical disc, and in particular relates toan optical pickup in an optical disc device. More specifically, thisinvention relates to an optical pickup equipped with a plurality ofobjective lenses, so as to enable recording onto and reproduction from aplurality of types of optical discs having different opticalcharacteristics.

2. Description of the Related Art

Various configurations have been devised for optical pickups for opticaldisc devices to enable recording and reproduction using a plurality oftypes of optical discs having different optical characteristics. Inparticular, due to the appearance of Blu-ray discs, which arehigh-density recording media, hereafter optical disc devices will besought which are capable of recording onto and reproduction fromblue-light optical discs (HD-DVD and Blue-ray discs) in addition toconventional red-light optical discs (CDs and DVDs).

In order to enable recording onto and reproduction from a plurality oftypes of optical discs having different optical characteristics using asingle optical pickup, a major issue is how to equip the optical pickupwith objective lenses. Two methods of resolving this problem are beingconsidered. One method involves equipment with a single objective lenswhich is compatible with the plurality of types of optical discs havingdifferent optical characteristics. The second method involves equipmentof a plurality of objective lenses, corresponding to the plurality oftypes of optical disc.

Next, the thickness of objective lenses corresponding to principaloptical discs is explained, referring to FIG. 14. In (A) of FIG. 14, thesymbol 101 denotes an objective lens compatible with DVDs and CDs. Thethickness Ta of this compatible objective lens 101 is approximately 1.3mm. The symbol 102 denotes a Blu-ray objective lens compatible withBlu-ray discs. The thickness Tb of this Blu-ray objective lens 102 isapproximately 2.5 mm. The symbol 103 denotes a BD/DCD/CD compatibleobjective lens, which can be used with DVDs, CDs, and Blu-ray discs. Thethickness Tc of this BD/DVD/CD compatible objective lens 103 isapproximately 4.5 mm. When the objective lens along accounts for this4.5 mm thickness, considering that the standing mirror is placeddirectly below the objective lens, there has been the problem that thethickness of the optical pickup becomes larger than the thickness ofslim drives (7.3 mm) used in notebook computers, which serve as oneyardstick of thinness.

Consequently, from the standpoint of reducing thickness, the second ofthe above methods (the method of equipping the pickup with a pluralityof objective lenses) is regarded as more effective for an optical pickupconfiguration enabling recording/reproduction of Blu-ray discs, DVDs andCDs.

FIG. 15 is a perspective view showing an actuator for an optical pickupdisclosed in Japanese Patent Laid-open No. 2003-281758. The actuator 100is a two-axis driving device in which objective lenses 112 and 113,corresponding to optical discs with different optical characteristics,are mounted on a single movable member 111, and the movable member 111can be driven independently in the focusing direction F and in theradial direction R. Such an actuator 100 can be applied to an opticalpickup for recording onto/reproduction from a plurality of optical discswith different optical characteristics.

The actuator 100 of Japanese Patent Laid-open No. 2003-281758 isstructured with the movable member 111 supported by a base 130 via aholder 114. Two objective lenses, 112 and 113, are mounted on themovable member 111, arranged in the radial direction R. The actuator 100comprises a support member 115, connecting the movable member 111 to theholder 114, and which supports the movable member 111 moveably in thefocusing direction F and in the radial direction R; first magneticcircuits 150, to move the movable member 111 in the focusing directionF; and second magnetic circuits 160, to move the movable member 111 inthe radial direction R.

As the manner of arrangement of the objective lenses 112 and 113, inconsideration of the fact that the data recording/reproduction region ofa high-density optical disc is positioned on the inner side comparedwith the data recording/reproduction region of a low-density opticaldisc, the objective lens denoted by the symbol 112 is placed so as to bepositioned on the inner side of the optical disc, as the lens for usewith high-density optical discs.

Two sets of each of the first and second magnetic circuits 150 and 160are positioned so as to surround on two sides the objective lenses 112,113 along the tangential direction (in the direction along thecircumference) T of the optical disc. Each set of the first magneticcircuits 150 comprises a focusing magnet 151 and a focusing coil 152;each set of the second magnetic circuits 160 comprises a tracking magnet161 and a tracking coil 162. The focusing magnets 151 and trackingmagnets 161 are permanent magnets; the focusing magnets 151 are providedfurther to the outside of the movable member 111 than the trackingmagnets 161. The focusing coils 152 are provided between the movablemember 111 and the focusing magnets 151; the tracking coils 162 areprovided between the movable member 111 and the tracking magnets 161.

An optical pickup which uses such an actuator 100 must necessarily beconfigured as shown in FIG. 16. That is, below the actuator 100 arepositioned a light source 140, which emits laser light L; a collimatorlens 141; a standing mirror 135 to guide the laser light L to theobjective lenses 112, 113; and a photodetector 143 to detect, for thelaser light L reflected by and returning from the optical disc outsidethe drawing, the quantity of light and similar. Between the light source140 and the standing mirror 135 is provided a half-mirror 142 totransmit laser light L from the light source 140 to the standing mirror135 and to guide laser light L which has been reflected by and returnsfrom the optical disc to the photodetector 143.

Laser light L emitted from the laser light source 140 passes through thehalf-mirror 142, is guided by the standing mirror 135 to one of theobjective lenses 112 or 113, and irradiates the recording surface of theoptical disc, held by the disc rotation mechanism. Laser light Lreflected by the recording surface of the optical disc passes through anobjective lens 112 or 113 and is reflected by the standing mirror 135,and is guided via the half-mirror 142 to the photodetector 143.

In an optical pickup using the above-described actuator of JapanesePatent Laid-open No. 2003-281758, as shown in FIG. 16, a standing mirrormust necessarily be positioned below the actuator, so that in order toachieve a thin shape, the magnetic circuits, standing mirror, and othercomponents must be made compact.

However, there are the problems that, when magnetic circuits are madecompact the driving performance in the focusing direction or the radialdirection declines, power consumption increases, and the trackingprecision declines, so that there are difficulties attending a compactdesign for magnetic circuits.

Further, the size of the standing mirror depends on the effectivediameter of the objective lenses; as optical design conditions, thewidth of the laser light beam reflected by the standing mirror must belarger than the effective diameter of the objective lens, so thatreduction of the size of the standing mirror and a thin design areextremely difficult to achieve.

SUMMARY OF THE INVENTION

The present invention has been proposed in light of the above-describedcircumstances. An object of the invention is to provide an opticalpickup which can easily be made compact and thin, without detractingfrom the electromagnetic performance or optical performance.

According to a first aspect of the present invention, there is providedan optical pickup for driving objective lenses in a focusing directionand in a radial direction. The pickup of the present inventioncomprises: a movable member including a center portion, a first side anda second side, the first side and the second side being apart from eachother in the radial direction so as to flank the center portion; aplurality of objective lenses provided at the center portion of themovable member; a first coil block and a second coil block provided atthe first side and the second side of the movable member, respectively;a first pair of magnets flanking the first coil block in a tangentialdirection perpendicular to both the focusing direction and the radialdirection; a second pair of magnets flanking the second coil block inthe tangential direction; a plurality of support members attached to thefirst side and the second side of the movable member in a manner suchthat the movable member is movable in the focusing direction and theradial direction; and a reflector facing the center portion of themovable member. Further, each of the coil blocks comprises a focusingcoil and a tracking coil. The focusing coil has a coil axis extending inthe focusing direction and is provided for driving the movable member inthe focusing direction, while the tracking coil has a coil axisextending in the tangential direction and is provided for driving themovable member in the radial direction. The tracking coil is provided onan outer side of the focusing coil. The center portion of the movablemember is thinner than the first side and the second side of the movablemember.

Preferably, each of the coil blocks may further comprise a tangentialtilt coil and a radial tilt coil. The tangential tilt coil is providedfor tilting the movable member about an axis extending in the radialdirection, while the radial tilt coil is provided for tilting themovable member about an axis extending in the tangential direction.

Preferably, the tangential tilt coil may have a coil axis extending inthe focusing direction and be provided adjacent to an open end of thefocusing coil. The radial tilt coil may have a coil axis extending inthe focusing direction and be provided adjacent to the other (oranother) open end of the focusing coil.

Preferably, each pair of the magnets may be arranged in a manner suchthat the paired magnets have opposite magnetic poles in the tangentialdirection.

Preferably, the plurality of objective lenses may be arranged side byside in the tangential direction.

Preferably, the reflector may comprise a plurality of standing mirrorscorresponding to the plurality of objective lenses, respectively. Thestanding mirrors are provided between the first coil block and thesecond coil block so that a laser beam propagating in the tangentialdirection is reflected toward the corresponding objective lenses.

Preferably, the optical pickup of the present invention may furthercomprise a holder for supporting the movable member in a cantilevermanner via the plurality of support members. The holder is formed with alight-guiding passage for allowing the laser beam to propagate in thetangential direction toward the standing mirrors.

According to a second aspect of the present invention, there is providedan optical disc devise incorporating the above-described optical pickup.

According to the present invention, it is possible to provide a compactoptical pickup that comprises the above-mentioned components (a movablemember, a plurality of objective lenses, etc.) without impairing theirproper functions. In particular, the center portion of the movablemember is made thinner than the sides flanking the center portion. Thus,the reflector (standing mirrors), facing the center portion, can bearranged very close to the center portion of the movable member, whichcontributes to reduction in thickness of the optical pickup.

Other aspects of the present invention and their advantages will beexplained in the following with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing an optical pickupaccording to a first embodiment of the invention;

FIG. 2 is an overall perspective view of the optical pickup shown inFIG. 1;

FIG. 3 is a front view showing a partially modified example of theoptical pickup shown in FIG. 1;

FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 2;

FIG. 5 is a schematic diagram to explain the operation of the opticalpickup shown in FIG. 1;

FIG. 6 is an exploded perspective view showing an optical pickupaccording to a second embodiment of the invention;

FIG. 7 is an overall perspective view of the optical pickup shown inFIG. 6;

FIG. 8 is a perspective view to explain the operation of the opticalpickup shown in FIG. 6;

FIG. 9 is a perspective view showing an optical pickup according to athird embodiment of the invention;

FIG. 10 is a perspective view showing an optical pickup according to afourth embodiment of the invention;

FIG. 11 is a cross-sectional view along line IX-IX in FIG. 10;

FIG. 12 is a plane view to explain an example of an objective lensmounting pattern;

FIG. 13 is a perspective view showing an optical disc deviceincorporating an optical pickup of the invention;

FIG. 14 is an explanatory diagram used to explain the thickness ofobjective lenses corresponding to various types of optical disc;

FIG. 15 is a perspective view showing an actuator for an optical pickupof the prior art; and,

FIG. 16 is a cross-sectional view taken along line XVI-XVI in FIG. 15.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 through FIG. 5 show a first aspect of an optical pickup of theinvention. The optical pickup A1 of this aspect is equipped with twotypes of lens, corresponding to a plurality of optical discs (forexample, Blu-ray discs, DVDs, and CDs) with different opticalcharacteristics, and are used for optical recording onto andreproduction from the optical discs. In each of the diagrams, the sideon which optical discs are positioned in the optical pickup A1 isconsidered as the upper side, the vertical direction is the focusingdirection F, the direction along the radius of the optical disc is theradial direction R, and the third direction along the circumference ofthe optical disc, which is perpendicular to both the focusing directionF and the radial direction R, is the tangential direction T.

As shown in FIG. 1 and FIG. 2, the optical pickup A1 has a movablemember 11; two objective lenses 12 and 13; a holder 14; a plurality ofsupport wires 15; two coil blocks 20, forming a pair; a base 30; twosets of magnets 31, each set having two magnets; and two standingmirrors 32 and 33. One coil block 20 comprises one focusing coil 21 andtwo tracking coils 22. The movable member 11, objective lenses 12 and13, holder 14, support wires 15, and coil blocks 20 are configured as anupper assembly; the base 30, magnets 31, and standing mirrors 32 and 33are configured as a lower assembly. The upper assembly and the lowerassembly are unified by fastening of the holder 14 and the base 30 to aseparate substrate (not shown) or similar.

The movable member 11 has a center portion 11A, in which are mounted theobjective lenses 12 and 13, and side portions 11B, extending on bothsides in the radial direction R from the center portion 11A, andcomprising the coil blocks 20. The center portion 11A is thinner thanthe side portions 11B, and is formed on the upper side than the sideportions 11B. In this center portion 11A are positioned the twoobjective lenses 12 and 13, arranged side by side in the tangentialdirection T. The side portions 11B have a space which penetrates in thefocusing direction F; a portion 30A of the base 30 (hereafter called the“core portion”) is inserted, as a magnetic core, in this space. Afocusing coil 21 is formed on the entire inner wall surface of the sideportions 11B, and tracking coils 22 are formed on the outer walls onboth sides, facing the tangential direction T. Protruding portions 11Care formed on the outside portions of the side portions 11B facing theradial direction R; to these protruding portions 11C are connected thetips of support wires 15 extending in the tangential direction T. Thebase ends of the support wires 15 are fastened to both end portions ofthe holder 14. By this means, the movable member 11 can move in thefocusing direction F and in the radial direction R, but cannot move inthe tangential direction T, to configure a so-called two-axis drivingsystem.

One of the objective lenses 12 is used for recording onto andreproduction from, for example, a first optical disc, and passes laserlight in the focusing direction F to focus the light on the firstoptical disc. The other objective lens 13 also passes laser light in thefocusing direction, but this objective lens 13 is used for recordingonto and reproduction from a second optical disc with opticalcharacteristics different from those of the first optical disc, andfocuses laser light at a wavelength different from that of the case ofthe first optical disc onto the second optical disc. These first andsecond optical discs generally have different optical characteristicspecifications, such as recording density and thickness dimensions;specifically, the disc types may be CDs, DVDs, HD-DVDs, or Blu-raydiscs. In this aspect, one of the objective lenses 12 corresponds to CDsand DVDs, and the other objective lens 13 corresponds to Blu-ray discs.It is desirable that one of the objective lenses be positioned such thata the straight line along the disc diameter coincides with a radius ofthe optical disc.

The holder 14 is of substantially the same thickness as the base 30, andis formed to be somewhat larger in the radial direction R than the base30. On both ends of the holder 14 extending in the radial direction Rare fastened base ends of support wires 15. This holder 14 is installedso as to be laterally adjacent to the base 30, with a prescribedinterval therebetween in the tangential direction T; the movable member11 is positioned so as to be superposed on the base 30 with an attitudeheld in the manner of a cantilever via the support wires 15.Consequently in the bottom portion of the holder 14 is provided alight-guiding hole or passage 14A to enable the unmodified propagation,to below the movable member 11, of laser light propagating in thetangential direction T from a light source, not shown.

As other examples of a light-guiding hole or passage 14A, variousaperture shapes can be adopted, as shown in (A) through (C) in FIG. 3;the size need only be sufficiently large to enable laser light to beincident on the standing mirror 32 even when there is some installationerror when assembling the optical pickup A1. As the aperture shape forthe light-guiding hole 14A, when taking performance and manufacturingcost into consideration, the shape shown in (A) of FIG. 3 is mostpreferable; but a rounded shape, may also be used in which the cornerportions 14B are gradually rounded, as shown in FIG. 2.

As stated above, the support wires 15 support the movable member 11 inthe manner of a cantilever; a plurality of support wires 15 are providedon one side portion 11B of the movable member 11. These support wires 15function as conducting wires to provide electricity to the focusingcoils 21 and tracking coils 22. The support wires 15 are provided in anumber necessary to drive the focusing coils 21 and tracking coils 22 onone side portion 11B of the movable member 11; in FIG. 1 and FIG. 2,three support wires 15 are shown on one side, but three or more supportwires may be provided.

The focusing coils 21 have an attitude such that the coil axis isextended in the focusing direction F, and are provided integrally on theside portions 11B of the movable member 11. The tracking coils 22 havean attitude such that the coil axis is extended in the tangentialdirection T, and are provided integrally on the side portions 11B of themovable member 11, positioned on the outsides of both focus coils 21.The focusing coils 21 are configured such that the electricallyconducting portions 21A in the position overlapping the tracking coils22 are readily affected by the action of the magnetic field due to themagnets 31, and the tracking coils 22 are configured such that, amongthe parallel electrically conducting portions through which currentflows in opposite directions in the focusing direction F, one of theelectrically conducting portions 22A is readily affected by the magneticfield of the magnets 31. Hence by causing a perpendicular magnetic fieldto act on the electrically conducting portions 21A of the focusing coils21, the movable member 11 is caused to move in the focusing direction F;and independently of this, by causing a perpendicular magnetic field toact on the electrically conducting portions 22A of the tracking coils22, the movable member 11 is caused to move in the radial direction R.

The magnets 31 are fastened to the base 30 at positions enclosing thecore portions 30A on two sides in the tangential direction T, thestanding mirrors 32 and 33 are fastened to the bottom-end portion, andthe base has a shape enabling placement of the movable member 11 betweenthe core portions 30A and magnets 31 and above the standing mirrors 32and 33. Cutout portions 30B to enable propagation of laser lightpropagating along the tangential direction T from a light source, notshown, unmodified to the standing mirrors 32 and 33, are provided in thelower portion of the base 30. Similarly to the light-guiding hole 14A,the cutout portions 30B can adopt various aperture shapes, as shown in(A) through (C) in FIG. 3.

The magnets 31 are fastened substantially in the four corners of thebase 30; two opposing magnets, enclosing a magnetic core portion 30A intwo sides in the tangential direction T, form a single set. The magnets31 forming one set are positioned such that the directions of themagnetic poles are in opposite directions in the tangential direction T;specifically, for example, all the magnets 31 are positioned such thatthe N pole is directed toward the magnetic core portion 30A. By thismeans, when two focusing coils 21 are driven such that the direction ofcurrent about the axis in the focusing direction F is the same, anelectromagnetic force acts in the same direction on the electricallyconducting portions 21A of each of the focusing coils 21, and the entiremovable member 11 is made to move in the focusing direction F. Thedisplacement at this time is controlled by adjusting the drivingcurrents in the focusing coils 21. And, if the tracking coils 22 aredriven such that the directions of the currents in the electricalconduction portions 22A of all the tracking coils 22 are the same asseen from the corresponding magnets 31, then an electromagnetic forcewith the same direction acts on the electrical conduction portions 22A,so that the entire movable member 11 is moved in the radial direction R.The displacement at this time is controlled by adjusting the drivingcurrents in the tracking coils 22. That is, the focusing coils 21 andmagnets 31 function as magnetic circuits for focusing control, and thetracking coils 22 and magnets 31 function as magnetic circuits fortracking control. Each of the magnets 31 is used in common for focusingcontrol and for tracking control. The magnetic circuits, combined withthe movable member 11, holder 14, support wires 15, and base 30 form anactuator. By means of this configuration, the optical pickup A1,provided with the necessary and sufficient electromagnetic functions,can be made thin and compact.

The standing mirrors 32 and 33 are embedded into the interior of andfastened to the base 30, and arranged to face the center portion 11A ofthe movable member 11 with the reflecting surfaces tilted toward therespective corresponding objective lenses 11 and 12. Each of thestanding mirrors 32 and 33 is positioned opposing the light-guiding hole14A of the holder 14 and a cutout portion 30B of the base 30 in thetangential direction T. One of the standing mirrors 32 is positioned soas to reflect upward laser light which has propagated in one directionalong the tangential direction T, to guide the laser light to theobjective lens 12. The other standing mirror 33 is positioned such thatthe reflecting surface is directed opposite the reflecting surface ofthe standing mirror 32, so as to reflect upward laser light which haspropagated in the direction opposite the former laser light along thetangential direction T, to guide the laser light to the objective lens13. These standing mirrors 32 and 33 intervene at least partiallybetween the two side portions 11B of the movable member 11, that is,between the pair of coil blocks 20, and to the extent that the centerportion 11A of the movable member 11 is positioned higher than the twoside portions 11B, the standing mirrors 32 and 33 are positioned asclosely as possible to the center portion 11A of the movable member 11.By this means, the thickness of the optical pickup A1 is stipulated bythe thickness of the holder 14 and base 30, and the standing mirrors 32and 33 do not increase the thickness of the optical pickup A1. As aresult the standing mirrors 32 and 33 are of a size necessary andsufficient, as a condition of optical design, for the width of the laserlight beam to be larger than the effective diameters of the objectivelenses 12 and 13, so that a compact and thin optical pickup A1 with thedesired optical performance can be realized. In this aspect, twostanding mirrors 32 and 33 are placed back-to-back; but a singlestanding mirror may be used, integrally formed with two reflectingsurfaces facing in opposite directions.

As shown in FIG. 4, the optical pickup A1 is incorporated into theoptical disc device (not shown) together with such other opticalcomponents as laser light sources 40A and 40B, collimator lenses 41A and41B, beam splitters 42A and 42B, and photodetectors 43A and 43B. Theoptical disc D is placed, supported by a spindle shaft (not shown) alongthe focusing direction F, such that the recording surface is opposed tothe optical pickup A1, and during recording and reproduction the opticaldisc D is rotated at high velocity about the spindle shaft. In FIG. 4,the radial direction R, not shown, is in the direction perpendicular tothe plane of the paper. The optical disc device also comprises opticalcomponents to cause the laser light to be incident more efficiently onthe objective lenses 12 and 13, or to efficiently guide light reflectedfrom the optical disc D to the photodetectors 43A and 43B; thesecomponents are likewise not shown.

When for example the laser light source 40A positioned on the left sidein the tangential direction T in FIG. 4 emits laser light L1, this laserlight L1 propagates to the right in the tangential direction T andpasses through the collimator lens 41A and beam splitter 42A, passesthrough the light-guiding hole 14A on the left side in the holder 14 andbase 30 and through a cutout portion 30B, and is incident withoutmodification on the left-side standing mirror 32. The laser light L1 isreflected upward in the focusing direction F by the reflecting surfaceof the standing mirror 32, and finally passes through the objective lens12 and irradiates the optical disc D. On the other hand, when the laserlight source 40B positioned on the right side in the tangentialdirection T emits laser light L2, this laser light L2 propagates to theleft in the tangential direction T, passing through the collimating lens41B and beam splitter 42B, passing through the light-guiding hole 14A onthe right side in the holder 14 and base 30 and through a cutout portion30B, and is incident without modification oh the standing mirror 33. Thelaser light L2 is then reflected upwards in the focusing direction F bythe reflecting surface of the standing mirror 33, and finally passesthrough the objective lens 13 and irradiates the recording surface ofthe optical disc D.

As actual operation, when an optical disc D is loaded into the opticaldisc device, laser light L1 and L2 is output simultaneously from boththe laser light sources 40A and 40B, and the laser light L1 and L2irradiate the recording surface of the optical disc D, and are reflectedat the irradiated positions. The reflected laser light L1 and L2 passthrough the respective corresponding objective lenses 12 and 13 in thedownward focusing direction F, proceeding in a manner opposite thatdescribed above to reach the beam splitters 42A and 42B, are reflectedby the beam splitters 42A and 42B, and are guided to the photodetectors43A and 43B.

At the photodetectors 43A and 43B, the quantities of light, diffractionpatterns, and similar of the reflected returning laser light L1 and L2are detected. Based on output signals from the photodetectors 43A and43B, a disc discrimination circuit, not shown, judges the type of theoptical disc D. When, as the discrimination result, it is judged thatthe currently loaded optical disc D is not recordable/reproducible, aread error results and the output of laser light from the laser lightsources 40A and 40B is halted.

When on the other hand the loaded optical disc D is for example a CD,the optical disc D is judged to be an appropriate CD, and recordingonto/reproduction from the optical disc D is performed using theleft-hand objective lens 12 and standing mirror 32, as well as only theoptical components 40A to 43A on the left side. Similarly, when forexample the loaded optical disc D is a Blu-ray disc, the optical disc Dis judged to be an appropriate Blu-ray disc, and the right-handobjective lens 13 and standing mirror 33, as well as only the opticalcomponents 40B to 43B on the right-hand side, are used to performrecording onto/reproduction from the optical disc D.

In recording onto/reproduction from the optical disc D, focusing errordetection processing and tracking error detection processing areperformed using the photodetectors 43A and 43B, and when a focusingerror is detected, the focusing coils 21 are driven to perform focusingcontrol. When a tracking error is detected, the tracking coils 22 aredriven to perform tracking control. This focusing control and trackingcontrol is realized through feedback control.

However, the optical disc D itself has such properties as warping andoscillation during high-speed rotation. Due to such properties of theoptical disc D, coma aberration may occur as a result of the tilt anglebetween the optical axis of the laser light L1 or L2 and the recordingsurface of the optical disc D, and if such coma aberration occursfrequently, it becomes impossible to secure stable low error ratecharacteristics during recording or reproduction. For example, in thecases of DVDs and Blu-ray discs, it is generally thought that the tiltangle must be within the range ±0.7°.

In order to satisfy such tilt angle requirements, in this aspect a pairof focusing coils 21 is used in feedback control, to control the tiltingabout the axis in the tangential direction T (radial tilt servo control)of the objective lenses 12 and 13 (movable member 11). That is, thefocusing coils 21 and magnets 31 are used for radial tilt servo controlin addition to focusing control.

Specifically, when performing radial tilt servo control, thephotodetectors 43A and 43B detect the radial tilt angle about the axisin the tangential direction T. Based on the detected radial tilt angle,the driving currents in the two focusing coils 21 are controlled suchthat a difference arises between the magnitudes of the electromagneticforces at the electrically conducting portions 21A, causing the radialtilt angle to become 0. By this means, the optical axis of the objectivelens 12 or 13 is controlled so as to always be perpendicular to therecording surface of the optical disc D, as seen from the tangentialdirection T. This radial tilt servo control is performed simultaneouslywith focusing control.

As shown schematically in (A) in FIG. 5, when the optical disc D iswarped in the radial direction R, if the force in the focusing directionF necessary for focusing control is F0 and the torque about the axis inthe tangential direction T necessary for radial tilt servo control isR0, then driving currents are made to flow in the electricallyconducting portions 21A (not shown) of the focusing coils 21 such thatthe electromagnetic forces Fa and Fb shown in (B) of FIG. 5 occur. Thatis, for one focusing coil 21 there are two electrically conductingportions 21A which receive the action of electromagnetic induction, andthe force F0 in the focusing direction F is the result of summation ofthe electromagnetic forces Fa and Fb occurring at all the electricallyconducting portions 21A, so that F0=2Fa+2Fb. And because electromagneticforces 2Fa and 2Fb with different magnitudes occur on either side of theaxis S which is the center of rotation of the movable member 11, and theforces act at a distance x from the axis S to the focusing coils 21, thetorque R0 about the axis in the tangential direction T isR0=(2Fa−2Fb)×x. Through the action of this force F0 in the focusingdirection F0 and torque R0 about the axis in the tangential direction T,the attitudes of the objective lenses 12 and 13 are controlled such thatthe optical axis is appropriate relative to the recording surface of theoptical disc D. The driving currents in the two focusing coils 21 canalso be controlled such that the electromagnetic forces are directed inopposite directions. Although not shown in FIG. 5, the tangentialdirection T is perpendicular to the plane of the paper. In FIG. 5, theextent of warping of the optical disc D and magnitudes of forces(lengths of arrows) are substantially emphasized in order to facilitateunderstanding.

Hence according to the optical pickup A1 of this aspect, the movablemember 11 and the standing mirrors 32 and 33 are combined so as tooverlap in the focusing direction F, and when seen in plane-view fashionfrom the focusing direction F, side portions 11B are positioned on themovable member 11 which integrally comprises coil blocks 20 betweenmagnets 31 positioned at the four corners, so that these components canbe positioned compactly, and the overall size and shape of the opticalpickup A1 can be kept thin and compact.

Further, while attempting to reduce the size and thickness of theoptical pickup A1, the individual components necessary for focusingcontrol and tracking control are designed with sizes sufficient to fullyachieve the electromagnetic performance and optical performancerequired, so that stable and precise control is possible.

Also, in addition to focusing control and tracking control, radial tiltservo control can also be executed, so that still more stable andprecise control is possible.

FIG. 6 through FIG. 8 show a second aspect of an optical pickup. In thefollowing explanation, constituent components which are the same as orsimilar to those already described are assigned the same symbols, andexplanations are omitted.

The optical pickup A2 of this aspect essentially has the sameconfiguration as in the first aspect. A major difference is theconfiguration of the coil blocks 20. One coil block 20 is configuredhaving two focusing coils 21, two tracking coils 22 (omitted in FIG. 8),two tangential tilt coils 23, and two radial tilt coils 24 (omitted inFIG. 6 and FIG. 7).

Whereas the tracking coils 22 are similar to those in theabove-described first aspect, the focusing coils 21 are used only forfocusing control, and two focusing coils are provided so as to beadjacent in the circumferential direction C. The tangential tilt coils23 are used for control (tangential tilt servo control) to control thetangential tilt angle at 0 by tilting the movable member 11 about theaxis in the radial direction R; the two coils are provided with anattitude such that the coil axis is extended in the focusing directionF, and adjacent to the open end on the upper side in the focusingdirection F of each of the focusing coils 21. The radial tilt coils 24are used in control (radial tilt servo control) to control the radialtilt angle at 0 by tilting the movable member 11 about the axis in thetangential direction T; the two coils are provided with an attitude suchthat the coil axis is extended in the focusing direction F, and adjacentto the open end on the lower side in the focusing direction F of each ofthe focusing coils 21. The support wires 15 are provided, on one sideportion 11B of the movable member 11, in a number necessary for drivingtwo focusing coils 21, two tracking coils 22, two tangential tilt coils23, and two radial tilt coils 24. In FIG. 6 and FIG. 7, four supportwires 15 are shown on one side; but five or more support wires may beprovided.

As operation, the focusing control and tracking control are similar tothose of the above-described first aspect, and are performed using thefocusing coils 21 and tracking coils 22. The tangential tilt servocontrol and radial tilt servo control are performed as follows.

As shown in FIG. 8, for example, two tangential tilt coils 23 on oneside are driven by passing currents in opposite directions about theaxis in the focusing direction F, and driving the tangential tilt coils23 in positional relations opposing in the radial direction R so thatthe current direction is the same. Then, electromagnetic forces appearin opposite directions (see the white-filled arrows) in the twotangential tilt coils 23 positioned on one side as seen from the axis inthe radial direction R, and the tangential tilt coils 23 positioned onthe other side. As a result, the objective lenses 12 and 13 mounted onthe movable member 11 receive a torque and are tilted about the axis rin the radial direction R. The tilt amount in this case is controlled byadjusting the driving currents in the tangential tilt coils 23.

On the other hand, for example the two radial tilt coils 24 on one sideare driven such that the direction of current about the axis in thefocusing direction F is the same, and moreover radial tilt coils 24 in apositional relation of opposition in the radial direction R are drivensuch that the direction of current is opposite. By this means,electromagnetic forces arise in opposite directions at the two radialtilt coils 24 positioned on one side as seen from the axis r in thetangential direction T and the two radial tilt coils 24 positioned onthe other side (see the black arrows). By this means, the objectivelenses 12 and 13 mounted on the movable member 11 feel a torque aboutthe axis t in the tangential direction T, and are tilted. The amount oftilt is controlled by adjusting the driving currents in the radial tiltcoils 24. Through such control of the tangential tilt coils 23 andradial tilt coils 24, the optical axes of the objective lenses 12 and 13are controlled so as to always be perpendicular to the recording surfaceof the optical disc.

Hence by means of the optical pickup A2 of this invention, advantageousresults similar to those of the first aspect can be obtained, and inaddition tangential tilt servo control can also be performedindependently of the radial tilt servo control, so that precise controlcan be executed with even greater stability, coma aberration can beeliminated to the extent possible, and stable low error ratecharacteristics can be secured.

FIG. 9 shows a third aspect of an optical pickup. The optical pickup A3of this aspect has a configuration which is basically similar to that ofthe second aspect. A difference is the different configuration of thefocusing coils 21 and radial tilt coils 24. One coil block 20 isconfigured having one focusing coil 21, two tracking coils 22 (omittedin FIG. 9), two tangential tilt coils 23, and one radial tilt coil 24.

One focusing coil 21 is provided on each side; two tangential tilt coils23 are provided on each side, so as to divide the open end on the upperside in the focusing direction F of the focusing coil 21. One radialtilt coil 24 is provided on each side, adjacent to the open end on thelower side in the focusing direction F of the focusing coil 21.

As the action, the focusing control, tracking control, and tangentialtilt servo control are similar to those in the second aspect, and theradial tilt servo control is executed as follows.

As shown in FIG. 9, with respect to the radial tilt coils 24 forexample, driving is performed such that the current directions areopposite. Then electromagnetic forces arise in opposite directions (seethe black arrows) at the radial tilt coil 24 positioned on one side asseen from the axis t in the tangential direction T and the radial tiltcoil 24 positioned on the other side. By this means, the objectivelenses 12 and 13 mounted on the movable member 11 receive a torque andare tilted about the axis t in the tangential direction T. The amount oftilt at this time can be controlled by adjusting the driving currents inthe radial tilt coils 24. This control of the radial tilt coils 24 issimilar to that in the second aspect, and the optical axes of theobjective lenses 12 and 13 are controlled so as to be alwaysperpendicular to the recording surface of the optical disc.

Hence according to the optical pickup A3 of this aspect, in contrastwith the second aspect, only one focusing coil 21 and one radial tiltcoil 24 are provided on each side, so that the coil structure can besimplified while achieving the same advantageous results as in thesecond aspect.

FIG. 10 and FIG. 11 show a fourth aspect of an optical pickup. Theoptical pickup A4 of this aspect has a configuration which is basicallysimilar to that of the first aspect. A difference is the fact that twoobjective lenses 12 and 13 are mounted on the movable member 11,arranged in the radial direction R. A single standing mirror 35 isprovided, so as to correspond to both the objective lenses 12 and 13.This standing mirror 35 is positioned so as to reflect upward the laserlight which has propagated from one side in the tangential direction Tvia the light-guiding hole 14A in the holder 14 and similar, to guidethe laser light to both the objective lenses 12 and 13. It is desirablethat two optical paths, passing through the objective lenses 12 and 13,be formed in parallel. In essence, a configuration is adopted in whichtwo optical systems, shown in FIG. 4 (laser light source, collimatorlens, beam splitter, and similar), are provided, arranged in parallel ononly one side in the tangential direction T. Of course a portion of theoptical components may be used in common. Or, as shown in FIG. 11, onelaser light source 40, collimator lens 41, beam splitter 42, andphotodetector 43 may be provided, with these optical components used incommon for different types of optical discs D. In this case, it isdesirable that a dichroic prism or other device having wavelengthselectivity be placed before the standing mirror 35 to switch theoptical path. In FIG. 11, an example in which the laser light source 40and similar are placed on the left side is shown as one example; ofcourse the laser light source and similar may be placed on the rightside, with the reflecting surfaces of the standing mirror placed so asto face the laser light source or similar. In this case, there is noneed to provide a light-guiding hole in the holder.

In addition to the patterns of mounting of the objective lenses 12 and13 shown in the above first through fourth aspects, mounting patternssuch as those of (A) through (F) in FIG. 12 may be used. For example, asshown in (A) and (B) in FIG. 12, two objective lenses 12 and 13 may beplaced so as to be arranged in a diagonal direction on the upper face ofthe movable member 11. Or, as shown in (C) through (F) in FIG. 12, threeor four objective lenses 12, 13 can be mounted on the movable member 11,with appropriate intervals therebetween. Whatever the pattern formounting the objective lenses 12 and 13, so long as positioning suchthat the movable member 11 and the standing mirror (not shown in FIG.12) overlap, the optical pickup can be made thin and compact.

The optical pickups A1 through A4 described in the above first throughfourth aspects are mounted on a traverse unit 50, provided within theoptical disc device A0 as shown in FIG. 13. The optical disc D is loadedinto the optical disc device A0 by inserting from the insertion aperture51, and this optical disc D is supported on a spindle shaft (not shown).The traverse unit 50 is supported by a pair of rails 52 on therecording-surface side of the optical disc D along a radial direction,and driving means 53 is provided to cause reciprocating motion of thetraverse unit 50 in a radial direction of the optical disc D along therails 52. By adopting in this optical disc device A0 an optical discpickup A1 to A4 which has been designed to be thin and compact, theentire optical disc device A0 can be made thin and compact.

1. An optical pickup for driving objective lenses in a focusingdirection and in a radial direction, the pickup comprising: a baseconfigured with an interior mounting space and a light-propagatingcutout; a movable member movable relative to the base, the movablemember including a center portion, a first side and a second side, thefirst side and the second side being apart from each other in the radialdirection so as to flank the center portion; a plurality of objectivelenses provided at the center portion of the movable member; a firstcoil block and a second coil block provided at the first side and thesecond side of the movable member, respectively; a first pair of magnetsprovided on the base and flanking the first coil block in a tangentialdirection perpendicular to both the focusing direction and the radialdirection; a second pair of magnets provided on the base and flankingthe second coil block in the tangential direction; a plurality ofsupport members attached to the first side and the second side of themovable member in a manner such that the movable member is movable inthe focusing direction and the radial direction; relative to the base; aholder configured with a light guiding opening and connected to thesupport members holding the movable member via the support members; areflector provided in the interior mounting space of the base, facingthe center portion of the movable member, and intervening between thefirst side and second side of the movable member; wherein each of thecoil blocks includes a focusing coil and a tracking coil, the focusingcoil having a coil axis extending in the focusing direction and beingprovided for driving the movable member in the focusing direction, thetracking coil having a coil axis extending in the tangential directionand being provided for driving the movable member in the radialdirection, the tracking coil being provided on an outer side of thefocusing coil, wherein the center portion of the movable member isthinner than the first side and the second side of the movable member,and wherein the light-guiding opening of the holder is aligned with thelight-propagating cutout of the base to allow a light beam to passthrough the light-guiding opening of the holder and thelight-propagating cutout of the base onto the reflector.
 2. The opticalpickup according to claim 1, wherein each of the coil blocks furtherincludes a tangential tilt coil and a radial tilt coil, the tangentialtilt coil being provided for tilting the movable member about an axisextending in the radial direction, the radial tilt coil being providedfor tilting the movable member about an axis extending in the tangentialdirection.
 3. The optical pickup according to claim 2, wherein thetangential tilt coil has a coil axis extending in the focusing directionand is provided adjacent to an open end of the focusing coil, and theradial tilt coil has a coil axis extending in the focusing direction andis provided adjacent to another open end of the focusing coil.
 4. Theoptical pickup according to claim 1, wherein each pair of magnets isarranged in a manner such that the magnets have opposite magnetic polesin the tangential direction.
 5. The optical pickup according to claim 1,wherein the plurality of objective lenses are arranged side by side inthe tangential direction.
 6. The optical pickup according to claim 5,wherein the reflector includes a plurality of standing mirrorscorresponding to the plurality of objective lenses, respectively, thestanding mirrors being provided between the first coil block and thesecond coil block so that a laser beam propagating in the tangentialdirection is reflected toward the corresponding objective lenses.
 7. Theoptical pickup according to claim 6, wherein the holder supports themovable member in a cantilever manner via the plurality of supportmembers, and the light guiding opening allows the laser beam topropagate in the tangential direction toward the standing mirrors.
 8. Anoptical disc devise comprising the optical pickup according to claim 1.9. An optical pickup for driving an objective lens in a focusingdirection and in a radial direction, the pickup comprising: a basehaving an interior mounting space and a light-propagating cutout; amovable member movable relative to the base, the movable memberincluding a center portion, a first side and a second side, the firstside and the second side being apart from each other in the radialdirection so as to flank the center portion; an objective lens providedat the center portion of the movable member; a combination of coils andmagnets for driving the movable member in the focusing direction and inthe radial direction; a holder to hold a movable member via a pluralityof support wires and configured with a light guiding opening; and areflector provided in the interior of the mounting space of the base,facing the center portion of the movable member, intervening between thefirst side and second side of the movable member, wherein thelight-guiding opening of the holder is aligned with thelight-propagating cutout of the base to allow a light beam to passthrough the light-guiding opening of the holder and thelight-propagating cutout of the base onto the reflector.
 10. An opticalpickup for driving objective lenses in a focusing direction and in aradial direction, the pickup comprising: a movable member including acenter portion, a first side and a second side, the first side and thesecond side being apart from each other in the radial direction so as toflank the center portion; a plurality of objective lenses provided atthe center portion of the movable member; a first coil block and asecond coil block provided at the first side and the second side of themovable member, respectively; a first pair of magnets flanking the firstcoil block in a tangential direction perpendicular to both the focusingdirection and the radial direction; a second pair of magnets flankingthe second coil block in the tangential direction; a plurality ofsupport members attached to the first side and the second side of themovable member in a manner such that the movable member is movable inthe focusing direction and the radial direction; and a reflector facingthe center portion of the movable member; wherein each of the coilblocks comprises a focusing coil and a tracking coil, the focusing coilhaving a coil axis extending in the focusing direction and beingprovided for driving the movable member in the focusing direction, thetracking coil having a coil axis extending in the tangential directionand being provided for driving the movable member in the radialdirection, the tracking coil being provided on an outer side of thefocusing coil; wherein the center portion of the movable member isthinner than the first side and the second side of the movable member;wherein each of the coil blocks further includes a tangential tilt coiland a radial tilt coil, the tangential tilt coil being provided fortilting the movable member about an axis extending in the radialdirection, the radial tilt coil being provided for tilting the movablemember about an axis extending in the tangential direction; and whereinthe tangential tilt coil has a coil axis extending in the focusingdirection and is provided adjacent to an open end of the focusing coil,the radial tilt coil having a coil axis extending in the focusingdirection and being provided adjacent to another open end of thefocusing coil.